Generally, commonly used electromagnetic valves and the like have contained the electromagnetic actuator as shown in FIG. 10. Such type electromagnetic actuator comprises a stationary core 1 fixed on a yoke 2, movable core 3 movably arranged with respect to the stationary core 1 so as to reciprocally move in the direction represented by the arrow 11, and coil 7 wound around the movable core 3 to generate the first magnetic flux 8 when the coil 7 is energized.
However, this type electromagnetic actuator is relatively poor in its sensitivity and thus can not generate required attractive force at a low current. The inventor of the present invention has already proposed improved electromagnetic actuators which can generate great moving force in spite of low current. This type electromagnetic actuators have been shown in PCT/JP84/00084, PCT/JP85/00313, PCT/JP85/00314, and PCT/JP85/00536.
This type of electromagnetic actuator further comprise a permanent magnet 5 in addition to the conventional device as shown in FIG. 10. In detail, as shown in FIG. 1 to FIG. 4, the permanent magnet 5 is secured to the yoke 2 or the movable core 3 so as to generate the second magnetic flux 9 which dividingly flows in parallel to the first magnetic flux 8 generated by the coil 7.
In the previously invented devices shown in FIG. 1, FIG. 2 and FIGS. 3(a), (b), the movable core 3 is reciprocally moved in the direction represented by the arrow 11 with respect to the stationary core 1.
In the previously invented device shown in FIG. 4(a) and FIG. 4(b), the movable core 3 is secured to a shaft 13a and can be rotatably moved in the direction represented by the arrow 11 with respect to the stationary core 1 through a journal 13b.
However, the above described devices shown in FIG. 1 to FIG. 4, previously proposed by the inventor of the present invention, can not always provide characteristics of a high sensitivity since it depends on the combination of values such as magnetomotive forces caused by the coil 7 and the permanent magnet 5 and magnetic reluctances of the permanent magnet 5 and in the gap between the movable core 3 and the stationary core 1 or the movable core 3 and the yoke 2.